According to the time-resolved spectra of lightning return stroke process and based on the plasma transmission theory,the evolution characteristics of the thermal conductivity and thermal diffusion coefficient of the ...According to the time-resolved spectra of lightning return stroke process and based on the plasma transmission theory,the evolution characteristics of the thermal conductivity and thermal diffusion coefficient of the discharge channel over time during the lightning return stroke are discussed.The radial distribution of the channel temperature in the lightning peak current phase is calculated,and the heat transfer along the radial direction of the channel is analyzed.The calculated transmission characteristic parameter values of the lightning discharge channel are all in a reasonable range.The results show that the heat transport coefficient of the lightning channel is closely related to the channel temperature and electron density.After returning to the peak current,the channel temperature slowly decreases,and the transport coefficient shows a non-linear and monotonous decay trend.The closer to the current core channel is,the greater the temperature gradient is,and the more the heat transferred radially outward is.展开更多
The discharge channel is a crucial diagnostic tool for identifying the properties of gas switches.However,single-view images cannot easily be used to inherently understand the discharge channel characteristics of trig...The discharge channel is a crucial diagnostic tool for identifying the properties of gas switches.However,single-view images cannot easily be used to inherently understand the discharge channel characteristics of trigger electrodes.A reconstruction method of the discharge channel in gas switches is proposed based on a multi-axis tomography technique,which uses very few projections of optical images to reconstruct the location of a multichannel discharge in annular electrodes.In this paper,an algorithm named TVM-OSEM(total variation minimization ordered subsets expectation maximization)is proposed,which can effectively remove artifact noise to improve the reconstruction accuracy of discharge channels.The method is validated against simulations of a radiator with high-density-difference boundary.The calculated discharge channel distribution from one experiment is presented.展开更多
Substations have a large number of signal transmission cables beneath the ground.Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field.Under high-amplitude ...Substations have a large number of signal transmission cables beneath the ground.Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field.Under high-amplitude impulsive currents,the dispersion of currents can cause soil discharge and thus cause unexpected distortions in an electromagnetic field.This paper focuses on the distortions of the electric field.In general,soil discharge channels occur in the vicinity of the independent rod.Closer development of the channel might enhance the electric field distribution and the potential surrounding the outer insulation of the cables(i.e.the surface potential on the cable).Therefore,this paper establishes a platform for observing the soil discharge channel and measuring the surface potential.Direction characteristic of the channel is extracted from the captured image of soil discharge channels and the surface potential is obtained by the measured coupling capacitive current on the shield experimentally.This paper also presents an improved model considering a dynamic growing discharge channel for the transient analysis of the grounding electrode.Study results show the surface potential increases as the discharge channel approaches the cable.To quantify this enhancement effect,the ratio of the highest to the lowest value of surface potential in different directions is taken as the multiple of the surface potential increase.The calculated multiples of the surface potential increase are in the range of 1 to 1.64 times under different conditions by the improved model.Therefore,taking the soil discharge channel into account is helpful to accurately analyze the impulsive interference of buried cables.展开更多
Needle-to-plane geometry has been widely investigated and used in underwater pulsed discharges.The position relationship between the needle tip and insulation layer significantly affects the discharge patterns.We carr...Needle-to-plane geometry has been widely investigated and used in underwater pulsed discharges.The position relationship between the needle tip and insulation layer significantly affects the discharge patterns.We carried out experiments on underwater pulsed discharge with the needle tip protruding from,recessing into,and flushing with the insulating tube.The results are as follows.First,underwater pulsed discharge has a strong randomness under the experimental conditions.Different discharge patterns appeared under the same experimental environment.Second,recession into the insulator surface led to a higher probability of occurrence but a lower strength of spark discharge than protrusion.Third,between the needle tip protruding from and recessing into the insulation material,the average speed of propagation of underwater pulsed spark discharge decreased by an order of magnitude.The study shows that the optimum length of needle tip protruding from the insulation layer is 1 mm to obtain a strong underwater pulsed spark discharge.展开更多
A numerical model capable of predicting flow characteristics in a compound channel was established with the 3-D steady continuity and momentum equations along with the transport equations for turbulence kinetic energy...A numerical model capable of predicting flow characteristics in a compound channel was established with the 3-D steady continuity and momentum equations along with the transport equations for turbulence kinetic energy and dissipation rate. Closure was achieved with the aid of algebraic relations for turbulent shear stresses. The above equations were discretized with implicit difference approach and solved with a step method along the flow direction. The computational results showing the lateral distribution of vertical average velocities and the latio of total flow in the compound channel agree well with the available experimental data.展开更多
文摘According to the time-resolved spectra of lightning return stroke process and based on the plasma transmission theory,the evolution characteristics of the thermal conductivity and thermal diffusion coefficient of the discharge channel over time during the lightning return stroke are discussed.The radial distribution of the channel temperature in the lightning peak current phase is calculated,and the heat transfer along the radial direction of the channel is analyzed.The calculated transmission characteristic parameter values of the lightning discharge channel are all in a reasonable range.The results show that the heat transport coefficient of the lightning channel is closely related to the channel temperature and electron density.After returning to the peak current,the channel temperature slowly decreases,and the transport coefficient shows a non-linear and monotonous decay trend.The closer to the current core channel is,the greater the temperature gradient is,and the more the heat transferred radially outward is.
基金supported by National Natural Science Foundation of China(No.11575147)the Distinguished Youth Fund(No.JQZQ021901)。
文摘The discharge channel is a crucial diagnostic tool for identifying the properties of gas switches.However,single-view images cannot easily be used to inherently understand the discharge channel characteristics of trigger electrodes.A reconstruction method of the discharge channel in gas switches is proposed based on a multi-axis tomography technique,which uses very few projections of optical images to reconstruct the location of a multichannel discharge in annular electrodes.In this paper,an algorithm named TVM-OSEM(total variation minimization ordered subsets expectation maximization)is proposed,which can effectively remove artifact noise to improve the reconstruction accuracy of discharge channels.The method is validated against simulations of a radiator with high-density-difference boundary.The calculated discharge channel distribution from one experiment is presented.
基金supported by the National Natural Science Foundation of China(51777020)supported by the Science and Technology Project of State Grid Corporation of China(“Study on the Transient Characteristics of Grounding System and the Test and Evaluation Method of Current Dispersion Performance Under the Successive Impulse Current”,5500-202026088A-0-0-00)。
文摘Substations have a large number of signal transmission cables beneath the ground.Both the insulation safety and signal reliability of the cables are affected severely by the electromagnetic field.Under high-amplitude impulsive currents,the dispersion of currents can cause soil discharge and thus cause unexpected distortions in an electromagnetic field.This paper focuses on the distortions of the electric field.In general,soil discharge channels occur in the vicinity of the independent rod.Closer development of the channel might enhance the electric field distribution and the potential surrounding the outer insulation of the cables(i.e.the surface potential on the cable).Therefore,this paper establishes a platform for observing the soil discharge channel and measuring the surface potential.Direction characteristic of the channel is extracted from the captured image of soil discharge channels and the surface potential is obtained by the measured coupling capacitive current on the shield experimentally.This paper also presents an improved model considering a dynamic growing discharge channel for the transient analysis of the grounding electrode.Study results show the surface potential increases as the discharge channel approaches the cable.To quantify this enhancement effect,the ratio of the highest to the lowest value of surface potential in different directions is taken as the multiple of the surface potential increase.The calculated multiples of the surface potential increase are in the range of 1 to 1.64 times under different conditions by the improved model.Therefore,taking the soil discharge channel into account is helpful to accurately analyze the impulsive interference of buried cables.
基金supported by the Science and Technology Research Project of the Hebei Higher Education Institutions of China No.ZD2014031。
文摘Needle-to-plane geometry has been widely investigated and used in underwater pulsed discharges.The position relationship between the needle tip and insulation layer significantly affects the discharge patterns.We carried out experiments on underwater pulsed discharge with the needle tip protruding from,recessing into,and flushing with the insulating tube.The results are as follows.First,underwater pulsed discharge has a strong randomness under the experimental conditions.Different discharge patterns appeared under the same experimental environment.Second,recession into the insulator surface led to a higher probability of occurrence but a lower strength of spark discharge than protrusion.Third,between the needle tip protruding from and recessing into the insulation material,the average speed of propagation of underwater pulsed spark discharge decreased by an order of magnitude.The study shows that the optimum length of needle tip protruding from the insulation layer is 1 mm to obtain a strong underwater pulsed spark discharge.
文摘A numerical model capable of predicting flow characteristics in a compound channel was established with the 3-D steady continuity and momentum equations along with the transport equations for turbulence kinetic energy and dissipation rate. Closure was achieved with the aid of algebraic relations for turbulent shear stresses. The above equations were discretized with implicit difference approach and solved with a step method along the flow direction. The computational results showing the lateral distribution of vertical average velocities and the latio of total flow in the compound channel agree well with the available experimental data.